byte[] messagebuffer = Encoding.ASCII.GetBytes(txtMessage.Text);
stream.Write(messagebuffer, 0, messagebuffer.Length);

socket = new Socket(AddressFamily.InterNetwork, SocketType.Raw, ProtocolType.IP);
socket.Bind(new IPEndPoint(IPAddress.Parse(comboBox1.SelectedItem.ToString()), int.Parse(tbPort.Text)));
socket.SetSocketOption(SocketOptionLevel.IP, SocketOptionName.HeaderIncluded, true);

byte[] byInc = new byte[] { 1, 0, 0, 0 };
byte[] byOut = new byte[4];
buffer = new byte[4096];
socket.IOControl(IOControlCode.ReceiveAll, byInc, byOut);
socket.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, OnReceive, null);